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Name ________________
Period _____
Periodic table trends
As you try to learn about the trends in the periodic table, there are two ways to
go about it.
1. Memorize trends
2. Understand the periodic table and what it means
Though memorizing the trends may seem easier to begin with, it is the
understanding of the periodic table that will lead to long-term success in
chemistry.
This sheet will attempt to have you come to an understanding of the periodic
table…
A few reminders…
1. Group = ___________
2. Period = ___________
Atom size moving down a group:
We learned when studying electrons that the period tells you the highest
__________ level an element’s electrons occupy.
And energy levels are basically ____________ from the nuclei.
Knowing that periods tell you the highest energy level occupied by electrons,
and that energy levels are distances from the nuclei, what happens to the size
of atoms as you increase the period number?
Draw atoms of the correct size in the group below:
Group 1
Period 1
Period 2
Period 3
Period 4
Period 5
Period 6
So as you go down a group, what happens to the size of the atoms of the
elements?
One way of measuring the size of an atom is to measure the atomic _________.
Atom size moving across a period:
A few reminders…
1. What is the charge on protons?
2. How does one determine the number of protons in an atom of an
element?
3. Opposites _______________
As you move across a period in the periodic table, what happens to the number
of protons in the atoms of elements?
If the number of protons in the atoms of the elements is increasing, what is
happening to the charge on the nucleus of atoms of an element as you move
across a period in the periodic table?
If the nucleus is becoming more and more positive moving across a period,
what effect will that have on the electrons? Will they want to be the same
distance from the nucleus, closer, or further?
Draw atoms of the correct relative size in the period below:
Group
1A
Group
2A
Group
3A
Group
4A
Group
5A
Group
6A
Group
7A
Group
8A
Period
2
Now put the two trends together and draw atoms of the correct relative size
below:
Group
1A
Period
1
Period
2
Period
3
Group
2A
Group
3A
Group
4A
Group
5A
Group
6A
Group
7A
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Group
8A
If you can keep in mind these two understandings,
you can use them to reason through all the trends
on the periodic table:
1. Moving down groups, you are adding energy
levels, or more distant electrons)
2. Moving across periods, you are adding protons
and more “pull” towards the nucleus.
Atomic radius (Size) trend:
Understanding
1. Moving down groups, you are
adding energy levels, or more
distant electrons
2. Moving across periods, you are
adding protons and more “pull”
towards the nucleus.
Result in size
Atomic radius (size) increases as you
move down a group, since you are
adding more electrons at further
distances (higher energy levels)
Atomic radius (size) decreases as you
move across a period, since the
increasingly positive nucleus “pulls” the
electrons closer.
I’ve drawn a simplified periodic table showing the atomic radii trends.
Ionization energy trend:
What is ionization energy?
Understanding
1. Moving down groups, you are
adding energy levels, or more
distant electrons
2. Moving across periods, you are
adding protons and more “pull”
towards the nucleus.
Result in ionization energy
Energy needed to pull electrons off
decreases moving down groups, since
electrons are further and further from
the (positive) pull of the nucleus.
Energy needed to pull electrons off
increases moving across periods,
since electrons are closer and closer to
the (positive) pull of the nucleus.
Draw a simplified periodic table showing the ionization energy trends.
Electronegativity trend:
What is electronegativity?
Understanding
1. Moving down groups, you are
adding energy levels, or more
distant electrons
2. Moving across periods, you are
adding protons and more “pull”
towards the nucleus.
Result in electronegativity
Ability to attract electrons decreases
as you move down groups, since the
nucleus (and positive charge for
attracting) is further and further away.
Ability to attract electrons increases as
you move across periods, since the
nucleus (and positive charge for
attracting) is becoming more and more
positive.
***The exception on this is the noble gases since they have stable electron
configurations
Draw a simplified periodic table showing the electronegativity trends.
Practice:
1. Which element in each pair has atoms with a larger atomic radius?
a. Sodium, lithium
b. Strontium, magnesium
c. Carbon, germanium
d. Titanium, zinc
e. Phosphorous, Aluminum
f. Barium, calcium
g. Hydrogen, radon
h. Silver, Molybdenum
2. Which element in each pair has a higher first ionization energy?
a. Lithium, boron
b. Magnesium, strontium
c. Cesium, aluminum
d. Barium, thalium
e. Fluorine, iodine
f. Gallium, bromine
g. Osmium, iron
h. Lead, silicon
3. Arrange the following groups in order of increasing ionization energy.
a. Be, Mg, Sr
b. Bi, Cs, Ba
c. Na, Al, S
d. O, Po, S
e. Ba, W, Au
4. Which element in each pair has a higher electronegativity?
a. Cl, F
b. C, N
c. Mg, Ne
d. As, Ca
e. Y, Rb
f. Sn, C
g. As, Mn
h. Fr, F
5. When the elements in each pair are chemically combined, which element
in each pair has a greater attraction for electrons?
a. Ca or O
b. H or O
c. O or F
d. K or S
e. Ca or Br
6. What’s the difference between first ionization and second ionization
energy?
7. From what you learned, what is the relationship between electronegativity
and first ionization energy?